Hydraulically activated servo device



Feb. 24, 1970 J. R. KOBELT HYDRAULICALLY ACTIVATED SERVO DEVICE Filed Nov. 27. 1967 Jack R. KOBELT, Inv tor y Q Agent United States Patent O 3,496,833 HYDRAULICALLY ACTIVATED SERVO DEVICE Jack R. Kobelt, 801 Main St., Vancouver, British Columbia, Canada Filed Nov. 27, 1967, Ser. No. 685,791 Int. Cl. F15!) 13/02 US. CI. 91-49 1 Claim ABSTRACT OF THE DISCLOSURE A hydraulically activated servo device to control, for instance, a throttle of a prime mover. A manually operated control rod admitting fluid under pressure to a hydraulic cylinder moving a spring retracted piston to a position according to the position of the control rod so that throttle position is according to and indicated by the position of the control rod.

FIELD OF THE INVENTION The present invention relates to a fluid servo device for use, for example, to control a throttle of a marine power plant.

Servos, particularly when used in marine installations, are required to be of simple construction so that maintenance and repair are minimized.

In the present invention, power is supplied by fluid under pressure admitted to the head of a cylinder thus causing a piston having a rod, herein called an actuating rod, to be urged outwards of an end wall of the cylinderthe throttle, or other control which is to be actuated, being operatively connected to the rod. The device is single acting in that fluid under pressure drives the piston in one direction only, the motion of the piston is however resisted by a compression spring. Hence when the pressure is relieved, energy stored in the spring moves the piston inwards retracting the actuating rod. I refer to the foregoing structure as including a single acting spring retracted piston.

The invention is characterized by means used; to admit fluid under pressure to act upon the cylinder head, thus urging the actuating rod outwards as above explained; to relieve the fluid pressure thus balancing the force of the spring when a particular extension of the actuating rod is attained, which extension is according to the position of a manually operated control rod; the said means also being adapted to release the pressure thus causing the operating rod to be retracted by the spring, the retraction also being according to the position of the manually operated control rod. Thus, the actuating rod is urged either by fluid pressure or by the spring, to a particular position according to the control position, with the manually operated control rod thus indicating, by its position, the position of for instance; a throttle lever operatively connected to the actuating rod.

SUMMARY OF THE INVENTION Basically, in the present invention the actuating, or piston, rod has a hollow bore having an open end to which the piston is secured, and a closed outer end. The operating rod is slidable within the actuating rod bore and extends outwards of the cylinder head, the outside diameter of the operating rod being a close fit to the diameter of bore aforesaid. The operating rod has a portion of reduced diameter, there being a shoulder at an end of the reduced diameter portion. When the control rod is in a position Where the shoulder is clear of the open end of the bore, fluid under pressure is free to pass into an annular space between the control rod and the bore through a hole in a wall of the hollow rod, thence to 3,496,833 Patented Feb. 24, 1970 ICC discharge through an outlet port of the cylinder. In the position described, there will be substantially no fluid pressure upon the piston head. Hence the piston, together with the actuating rod thereto attached, will be retracted by the spring until it reaches the end of its stroke, or until it reaches a position whereat the shoulder enters the bore, at which time the piston will come to rest at a point of equilibrium. It is seen that. as the control rod is moved, the actuating rod is urged to move following the motion of the control rod.

In an alternative embodiment, the control rod, extending slidably outwards through the cylinder head, terminates at an inner end at the position of the shoulder aforesaid-the actuating rod and the control rod being axially aligned so that the latter can slidably enter the bore of the former. The action of an embodiment having this alternative control rod is as before described, the fluid under pressure acting upon the cylinder head when the inner end of the control rod enters the bore, and being free to pass through the bore to discharge when the inner end is clear of the bore.

DESCRIPTION OF THE DRAWINGS FIGURE 1 is an end elevation of the invention.

FIGURE 2 is a section on line 22 of FIGURE 1.

FIGURE 3 is a block diagram indicating schematically how the invention may be used as a throttle control in a typical marine installation.

FIGURE 4 is a fragmented section showing alternative control rod construction.

Examples of practical embodiments of the invention are described below with reference to the drawings, the invention being capable of expression in structure other than that particularized herein.

DESCRIPTION RELATED TO FIGURE 2 Referring particularly to FIGURE 2, a hydraulic control device according to the invention has a cylinder 11 having an outer end wall 12. A piston rod, hereinafter referred to as an actuating rod, is designated by the numeral 13, which rod extends through the outer end wall 12 slidable of a suitable opening 13A of the outer end wall. A clevis 14 is obviously secured to an outer extremity of the said actuating rod, and a piston 15 is rigidly secured to an inner end thereof. A helical compression spring 16 urges the piston against an inner end wall 17A of a cylinder head 17.

The actuating rod 13 has a hollow bore, as seen at 18, to receive a control rod 19 slidable within the bore, the outside diameter of a control rod portion 20 being a close fit to the bore 18. The control rod outer portion 20, an outer end of which is threaded as seen at 21, is slidable of an opening 22 of the cylinder head 17. The control rod 19 has a portion 23 of reduced diameter extending between a head portion 24 and the outer portion 20. The outside diameter of the head portion is also a close fit to the bore 18.

The head portion 24 is grooved longitudinally as seen at 24A, to avoid piston action of the head 24. This enables air, or other fluid, to pass freely through the head rather than being entrapped between the head and an inner end wall, 18A, of the bore 18. Alternatively, a hole may be drilled axially through the head, or a fiat may be provided in lieu of the groove, to attain equivalent results, that is, means to prevent piston action of the head. The equivalents above are not shown.

The cylinder head 17 has an inlet port 25 threaded as seen at 26 to receive a standard hydraulic connection, not here shown. An adjustable needle valve 27 coopcrating with a seat portion 28 of the inlet port 25 serves to regulate admission of hydraulic fluid, entering the inlet port as indicated by the directional arrow 29. The

outer end wall 12 of the cylinder is provided with an outlet port 30 threaded as seen at 31 to receive a standard hydraulic fixture, not here shown.

The rod portion 20 is provided with an inner snap ring 32, and an outer snap ring 33, the travel of the control rod 19 being limited by the said inner and outer snap rings reaching inner and outer faces 34, 35, of the cylinder head 17.

Aligned openings 36 and 37 are provided in outer walls of the hollow bore 18. Leakage of hydraulic fluid is prevented by the several sealing means 39, which are of a form well known in the art. The piston 15 is provided with a cup seal 40, also of a form well known in the art. It is seen that the cylinder head 17 has a domed recess 41, so that the end wall surface 17A of the cylinder head is separated axially from the inner face 34, the axial separation of these two Surfaces being, in a typical installation, about an inch and one-half. The spacing of the inner and outer snap rings 32 and 33, taking into consideration the thickness of the cylinder head is such as to permit sliding axial motion of the control rod of about one and three-quarter inches.

OPERATION The operation of the device is as follows.

Referring to FIGURE 2, the control rod 19 is shown fully extended outward, that is to say with the snap ring 32 against the cylinder head surface 34. In this position, hydraulic fluid entering the inlet port 25 will pass freely through an annular space 42 defined by inner walls of the actuating rod bore 18 and outer walls of the reduced diameter portion 23 of the control rod 19, thence to pass through the openings 36, 37 of the actuating rod 13, to discharge through the outlet port 30 as indicated by the arrow 43. Discharge may be to a reservoir. not shown, and is commonly at atmospheric pressure, Thus, in the position described, there will be no unbalanced force tending to urge the piston inwards to compress the helical spring 16, and the actuating rod 13 will not move.

Let the control rod 19 be moved manually inwards a short distance (i.e., to the left as seen in FIGURE 2) until a shoulder 44 of the outer portion 23 of reduced diameter, enters the annular space, thus preventing passage of the hydraulic fluid through the said space. In these circumstances, the pressure of the hydraulic fluid acting upon the surface of the piston 15 will urge it to the left, extending the actuating rod 13 outwards and compressing the helical spring 16. This outwards motion will continue until such time as the shoulder 44 clears the outer surface of the piston, thus again permitting passage of the hydraulic fluid into the annular space aforesaid and so relieving the pressure of the hydraulic fluid tending to urge the piston inwards. It is seen that a position of equilibrium will be reached at which the piston 15, and accordingl the actuating rod 13, will remain stationary. Upon moving the control rod 19 further inwardsan equilibrium position having been established as abovethe actuating rod will move further outward in the above described manner, until the shoulder 44 again clears the piston face where a new equilibrium position will be reached. From the foregoing, it will be clear that the control rod having been moved fully inwards to the left-or to some intermediate position upon it being withdrawn, that is to say moved outwards, the control rod will move inwards until equilibrium position is reached. That is, the motion of the actuating rod will follow that of the control rod, the actuating rod being moved outward hydraulically, and being retracted by power stored in the compression spring during the outward motion. Thus the device effects power operation of, for instance a throttle or governor, operatively connected to the actuating rod.

The required strength of the spring 16 will vary in accordance with the particular installation, and is to be amply strong to cause the actuating rod to retract against any load caused by a particular control which is to be operated. The force with which the actuating rod 13 is urged outwards is equal to the pressure of the hydraulic fluid times the piston area, less the spring force. These factors are matters of design to be determined for a particular installation or class of installations, Speed of travel of the actuating rod is adjustable by the means of the needle valve 27 FIGURE 2, regulating the rate of admission of the fluid to the cylinder head.

DEVICE USED AS THROTTLE CONTROL, FIGURES 1 AND 3 When the hydraulic control device is used for instance to actuate the throttle or governor of a marine engine, the clevis 14 is connected to a suitable part of the throttle linkage, or to an intermediate linkage.

It is convenient that the device be mounted on brackets 45 and 46 FIGURE 1, to which brackets the device is secured suitably by trunnion mounts 47 and 48. The control rod 19 may be fitted with a knob, not shown, or alternatively linkage may be connected to the threaded portion 21 for operation at a remote position, as may be convenient. There are many suitable however these form no part of my invention, and therefore, are not further described.

FIGURE 3 is a diagrammatic representation of a hydraulic control device according to the invention, used to control the governor or throttle gear of a marine engine, individual parts being represented schematically, and not at a common scale. FIGURE 3 shows a marine engine 49, having a governor or throttle 50 operated by a lever 51. The hydraulic control device 10 is mounted upon brackets 45 secured to the hull of the craft, and the clevis 14 of the actuating rod 13 is secured to the lever 51. Thus power operated action of the throttle or governor gear is achieved by motion of the control rod 19.

A purpose of the particular construction of the control rod 19 described and illustrated is to maintain axial alignment with the actuating rod bore 18. This purpose is attained by the head portion 24, FIGURE 2.

ALTERNATIVE EMBODIMENT, FIGURE 4 An alternative embodiment is shown in FIGURE 4, wherein a control rod 19.1 terminates at an inner end 44.1 the position of which is the same as that of the shoulder 44 in FIGURE 2. In the FIGURE 4 construction, the end 44.1 is tapered as seen at 52, and an outer end of the actuating rod is shown correspondingly tapered internally at 53. This is to facilitate entry of the control rod 19.1 to the bore 18 since, if such an equivalent structure were not provided, alignment of the two rods would have to be maintained, even when wear has taken place, within nearly exact limits. Alternative to the corresponding tapers 52 and 53 illustrated, a single taper may be provided, i.e. either the taper 52 or the taper 53.

The action of the FIGURE 4 embodiment, or of the alternative single taper equivalents, is as previously described.

I claim:

1. A fluid operated servo device including in combination,

(a) a single acting spring retracted piston movable within a cylinder,

(b) an actuating rod having a longitudinal bore extending from an open end of the rod to a closed end thereof, the closed end of the rod extending slidably through an end of the cylinder, the piston being secured to the open end of the actuating rod, 9. side wall of the bore having an opening for the passage of fluid therethrough to a discharge port of the cylinder, and needle valve means to regulate rate of entry of the fluid to the cylinder head,

(0) a control rod axially aligned with and slidable of the bore, and extending slidably through a head of the cylinder, the control rod having a portion of reduced diameter defining, with the bore side wall, an annular space for the passage of fluid to discharge as aforesaid, an outer end of the reduced diameter portion being defined by a shoulder portion, constructed and arranged so that the shoulder portion entering the bore reduces the fluid pressure,

(d) and means to limit the range of slidable motion of the control rod,

(e) the control rod having a head portion defining an end of the reduced diameter portion remote from shoulder, the head portion being adapted to maintain the aforesaid axial alignment, and means to provide free passage of fluid past the head,

constructed and arranged so that inward movement of the control rod causes a portion thereof to enter the bore, whereupon the pressure of the fluid acts upon the piston urging it and the actuating rod to move outwards overcoming the retracting spring force, and so that when the piston has so moved until the control rod portion aforesaid is clear of the bore, the fluid flows through the bore thus reducing the fluid pressure upon the piston to equilibrium with the retracting force of the spring.

References Cited UNITED STATES PATENTS PAUL E. MASLUSKY, Primary Examiner US. Cl. X.R. 

